Telecommunications systems are carrying increasing amounts of information, both in the long distance network as well as in metropolitan and local area networks. At present data traffic is growing much faster than voice traffic, and will include high bandwidth video signals. In addition to the requirement for equipment to carry increasing amounts of telecommunications traffic there is a need to bring this information from the long distance network to businesses and to locations where it can be distributed to residences over access networks.
The equipment which has been developed to carry large amounts of telecommunications traffic includes fiber optic transport equipment which can carry high speed telecommunications traffic. The data rates on fiber optic systems can range from millions of bits per second (Mb/s) to billions of bits per second (Gb/s). In addition, multiple wavelengths of light can be carried on an optical fiber using Wavelength Division Multiplexing (WDM) techniques.
The ability to carry large amounts of telecommunications traffic on an optical fiber solves the long-distance point-to-point transport problem, but does not address the issue of how to add and remove traffic from the high-speed data stream. Equipment for adding and removing traffic has been developed and is referred to as “add-drop” multiplexing equipment.
Traditional designs for add-drop multiplexers are based on the use of multiple interface cards which receive high speed data streams, create a time division multiplex signal containing the multiple data streams, and route the time division multiplex signal to a cross-connect unit which can disassemble the data streams, remove or insert particular data streams, and send the signal to another interface card for transmission back into the networks. By aggregating the multiple data streams into a time division multiplexed data signal, the data rate of the time division multiplexed signal is by definition several times the rate of the maximum data rate supported by the interface cards. Such solutions have proven adequate for interface data rates in the range of 155 Mb/s to 622 Mb/s, but for data rates over 1 Gb/s there are a number of problems which arise due to the transport of and timing of the multiplexing and transmission of the high speed signals between cards in the cross-connect. Optical signals of 2.4 Gb/s have become a standard and there is a need for cross-connect equipment which can support multiple 2.4 Gb/s data streams.
Standardized interfaces and transmission hierarchies for telecommunications signals have been developed and include the pleisochronous digital hierarchy (PDH) standards, the Synchronous Digital Hierarchy (SDH) standards, and the Synchronous Optical Network (SONET) standards. In addition to these telecommunications transport standards and systems data standards and systems have been developed for interconnecting businesses and computers within businesses. These metropolitan and local area network (MAN/LAN) standards include Ethernet, Gigabit Ethernet, Frame Relay, and Fiber Distributed Data Interface (FDDI). Other standards, such as Integrated Services Digital Network (ISDN) and Asynchronous Transfer Mode (ATM) have been developed for use at both levels. Although individual pieces of equipment can be purchased to support telecommunications or MAN/LAN standards, these devices generally either connect data streams using a signal protocol or convert entire data streams from one protocol to another. There is a need for a device which can establish interconnectivity between interfaces at the MAN/LAN level, while providing cross-connection to the telecommunications PDH/SDH/SONET network.
Multiple interfaces are presently supported in cross-connect equipment by the use of different interface cards. For high-speed signals, these cards must be inserted into particular slots in order to insure that the signal can be transported between the interface card and the cross-connect unit and to another interface card. It would be desirable to have a cross-connect system in which cards can support high-speed optical signals of at least 2.4 Gb/s in any card slot.
It would also be useful to have a system which would support routing, bridging, and concentration functions within MANs/LANs, as well as permitting access to the telecommunications PDH/SDH/SONET network.
Because of the high data rates and amount of traffic carried in the telecommunications signals, it is necessary to insure that there are redundant interface units in the cross-connect, and that a protect interface card can be used if a working interface card fails.
For the foregoing reasons, there is a need for flexible cross-connect with a data plane that can support multiple high speed optical interfaces in any card slot, can establish connectivity between data cards and the transport network and which provides adequate protection against failed units.